I'll mention two things...
1 - this is a very old thread that has been revived. For the Brazilian ticket especially, maybe it should be made a new thread or merged with one about domestic Brazilian pricing and PAYMENT
2 - For domestic flights in Brazil, I usually find the Brazilian site gives much better prices than international site (sometimes the difference will be BRL1 to USD1). There do not seem to be restrictions as to who can buy domestic fares, per se. But the payment system has not accepted non-Brazilian cards/bank accounts, meaning the payer has to be Brazilian. As of today I see that maybe international cards are accepted (I've not tested - it used to be impossible) but still they require a CPF, which is basically a financial ID/tax ID for Brazil. As a North American, I've worked around this by either having a friend buy my ticket (using his CPF - he's not the passenger, just the one paying), or (less optimal) having a Brazilian travel agent make the purchase. An agent can take international payment for a domestic ticket on domestic pricing, but with a typical Brazilian travel agent the added fee is 10-20%. But paying 10-20% more is better than paying 5x... so I have done it.
Finally just to add, in the Brazilian market LATAM is the only one left doing this. GOL lets me buy using any card just as I would as a Brazilian. Azul as well. I used to prefer LATAM for airport/onboard service, but the latest GOL flights I bought have given me space to reconsider. The people working there care. Azul I haven't flown in a couple years, but I was very pleasantly surprised on the few flights I took. And both have an easy, NORMAL booking process. Not one where you can't buy Brazilian fares as a non Brazilian, not one where even on the international sites often they block your payment and then force you to go to a city ticket office to buy (I had this happen twice).
I do hope LATAM fixes this, but it's been a problem for many years now, and I've seen little to suggest they care about it.